Why a big tree yields less wood than it looks like it should
A 20 inch tree with 32 feet of usable stem looks like an enormous amount of timber standing up. Scale it and you get roughly 290 board feet on the Doyle rule and about 363 on the International rule. That is two logs. It is a decent stack of boards and it is nothing like what people picture, and the gap has three causes that stack up.
The first is that merchantable height is not total height. A 70 foot yard maple might have 16 feet of stem before the first big fork, and everything above the fork is firewood no matter how much of it there is. The second is taper. A log is scaled on its small end, not its middle, so every inch the stem narrows over its length is volume the rule refuses to count. The third is the rules themselves, and the Doyle rule especially is unkind to anything under about 20 inches.
Three rules, three answers
A log rule is an attempt to predict how many board feet of lumber a mill will actually saw out of a log of a given small-end diameter and length. They were built at different times for different equipment and they disagree, sometimes sharply.
| Small end, 16 ft log | Doyle | Scribner | International 1/4 in |
|---|---|---|---|
| 10 in | 36 | 55 | 65 |
| 12 in | 64 | 86 | 97 |
| 16 in | 144 | 166 | 181 |
| 20 in | 256 | 272 | 290 |
| 24 in | 400 | 403 | 425 |
Read down the 10 inch row. Doyle says 36 board feet, International says 65 — nearly double. Read the 24 inch row and they are within six percent. Doyle underestimates small logs badly and converges on the others as logs get big, which is exactly the behaviour you would expect from a rule that subtracts a fixed four-inch slab allowance regardless of log size. International 1/4 inch is built from a geometric model of a tapering log with a defined kerf, and it is generally the closest of the three to what a modern mill actually recovers.
None of this is a moral question. The rule is a unit, like a bushel. What matters is that the rule is named in the sale agreement, that you and the buyer are using the same one, and that you know which way the difference runs. On a stand of small logs, a buyer scaling Doyle and a seller thinking International are having two different conversations about the same pile.
Cubic volume, and why cords are a different question
Board feet are a lumber-recovery estimate. Cubic feet are a measurement of wood. For firewood, pulp and chips, the cubic figure is the useful one, and this calculator gets it by treating the stem as a cylinder of the breast-height diameter and multiplying by a form factor — the fraction of that cylinder the real tapering stem actually fills. Around 0.40 for a short, hard-tapering open-grown tree; around 0.50 for a long clean forest-grown bole.
Converting to cords adds another layer of approximation, because a cord is 128 cubic feet of stack, air included. Roughly 80 cubic feet of that is solid wood in a normal split stack, less for round or crooked pieces and more for straight-split wood laid tightly. If you want to work backwards from a stack you have already built rather than forwards from a standing tree, the firewood cord calculator does that directly, and the firewood seasoning and BTU calculator handles what that wood is worth as heat once it dries.
Measuring the inputs without a forester
Diameter at breast height means 4.5 feet above ground, measured on the uphill side on a slope. A tape around the trunk divided by pi gives the diameter; a 63 inch circumference is a 20 inch tree. Merchantable height is the judgement call — sight up the stem to the first defect, fork, or big limb that would stop a log, and estimate that height rather than the whole tree. If you have measured total height with the tree height calculator, merchantable height is usually a good deal less than half of it on an open-grown tree and can be two thirds or more on a forest-grown one.
Taper is the input people guess worst. A forest tree that grew in competition with a long clear stem might lose only an inch over 16 feet. A field tree that has had light on all sides its whole life can lose three or four. If you have a felled stem to hand, measure it at both ends and you will never guess again. Board feet you already own, rather than board feet standing up, are the board foot calculator, and their weight for moving them is lumber weight.
Where this calculator stops
It measures and it sizes. It does not tell you whether a tree is safe or hazardous, and no number on this page should be read as saying so. Tree risk assessment is a professional discipline with its own training and its own vocabulary, and it depends on defects, species, targets and site history that a form cannot see.
The other line is the work itself. Felling a tree kills people every year, and it kills experienced people, not only beginners. So does anything done off the ground. A tree under tension does not behave the way it looks — a leaning stem, a hung-up top, a bent sapling or a limb pinned by another one holds stored energy that releases in a direction you did not choose. A chainsaw injury an hour from a road is a categorically different problem from the same cut in a shop with a phone and a driveway. Nothing on this site gives felling, notching, limbing or rigging technique, and none of it is a substitute for training.
Any tree near a structure, a fence line, a road or a power line belongs to a qualified arborist. Utility clearance work in particular is restricted to trained line-clearance crews in most places, and the reason is that electricity crosses a gap to a conductive object such as a wet branch or an aluminium ladder without being touched.
Before a tree becomes logs
One more thing that catches people out: in a great many places you need a permit to remove a tree, including a tree on land you own, and in some places to prune one over a certain size. Protected species, heritage listings, conservation overlays, subdivision covenants and street-tree rules all exist and none of them are consistent between jurisdictions. This page cannot tell you which apply to you and does not try. Ask your local authority before the saw comes out, because the penalties are usually assessed on the tree rather than on the intent.
Trees on or near a boundary are a legal question before they are a horticultural one. Who owns a trunk that straddles the line, what you may do to branches or roots that cross it, and what you owe a neighbour if your cutting kills their tree are all answered by local rules and, sometimes, by where the line actually runs rather than where the fence does. Cutting a neighbour's roots or branches has consequences that can run well past the cost of the tree. If the line matters, get a survey and read the local rules before anyone starts.
Questions people ask
Which log rule should I use?
The one the person paying you is using, and you should establish that before anything is cut. In much of the eastern and southern United States hardwood is bought on Doyle; Scribner is common in the west and on federal timber; International 1/4 inch is the usual choice for research, for extension work, and increasingly for anyone who wants the number to resemble what the mill recovers. If you are sawing the logs yourself on your own mill, use International or just work in cubic feet, because a scale rule is a trading convention and you are not trading. If a buyer will not name the rule in writing, that itself is information.
Why does my tree scale to zero board feet?
Almost always because the stem drops below the minimum top diameter before a full log length fits inside the merchantable height, and the calculator will say so. Three things fix it and each of them is a real decision rather than a fudge: cut shorter logs, accept a smaller top diameter, or accept that the tree is firewood. Doyle contributes to this too — its scale falls to nothing around a 6 inch top, because the rule subtracts four inches for slabbing before it squares anything, and a 6 inch log has very little left after that.
Is merchantable height the same as the height of the tree?
No, and mixing them up is the single biggest error in the inputs on this page. Merchantable height is the length of stem you could actually cut into logs: from the stump cut up to the first fork, big limb, sweep or defect that stops a log, or to the point where the stem narrows past your minimum top. On an open-grown yard tree with a low crown, that can be a fifth of the total height. On a forest-grown tree in a closed stand it might be two thirds. Total height goes in the tree height calculator; only the stem length goes here.
How much firewood is in the top and the limbs?
Enough to matter and too variable to predict well, which is why it is an input on this form rather than a fixed number. A crown-heavy open-grown maple can carry a third of its wood volume above the merchantable stem; a slender forest conifer with a small crown carries much less. The 35 percent default is a middle figure to be adjusted, not a species constant. The other thing the figure hides is labour: limb wood is small, crooked, full of knots and slow to buck and split, so a cord of it costs far more of your day than a cord out of a straight bole.
Does the calculator account for rot, sweep or metal in the trunk?
No. It scales a sound, straight, cylindrical-with-taper stem, which is a model. Real logs get deducted at the landing for heart rot, ring shake, sweep, crook, seams and old wounds, and a hollow butt log on a big yard tree is common enough that buyers price the risk in. Embedded metal is its own category: a tree that grew next to a fence, a clothesline or a nail-in sign can carry steel that will destroy a bandsaw blade, and many mills will not accept yard trees at all for that reason. Assume a deduction rather than assuming the calculator figure.